Limb amputation can result in profound disability, for which the most effective treatment is replacement of the missing limb with a prosthetic device. Effective options for treatment include body-powered prostheses, which rely on Bowden cables to translate gross body movements into control signals; and myoelectric prostheses, which are controlled by myoelectric signals (also called electromyographic or EMG signals) received from residual muscles of the individual with an amputation. Myoelectric signals are small electrical signals that propagate through a muscle as a result of nerve impulses, which causes contraction of the muscle fibers. Control of myoelectric prostheses relies on the detection of these signals through electrodes on the skin surface such that the voluntary contraction of a muscle can be used to actuate a specific intended movement in a prosthetic device attached to the individual with an amputation. The small voltage detected (typically 10 μV-1 mV) is conditioned electronically to render it suitable for actuation and control of the required motors in the prosthetic device. Typically, signal conditioning may be provided at the electrode contact site or within a separate electronic processing system. In either case, signals must be transmitted from the electrode to the control system of the prosthesis via wires or leads.
Prosthetic devices controlled by myoelectric signals have been under development since the late 1950s and have found a prominent place in the commercial market. Myoelectric control eliminates much of the prominent and uncomfortable harnessing necessary for body-powered control and reduces the effort required by the wearer to actuate the limb; however, use of a myoelectric device requires physical contact between the electrode and the skin surface.
Individuals with amputations may be fitted with a conventional gel liner, which is a soft insert placed between the residual limb and prosthetic socket that provides cushion to the limb and helps suspend the prosthesis. Some conventional gel liners may be constructed from a variety of materials such as urethane, silicone, or thermoplastic elastomers and are configured to provide a tight-fitting, compliant interface between the residual limb and the hard outer socket. Gel liners can be easy to roll onto the residual limb and provide increased comfort. In addition, some or all relative movement—and resulting friction—between the limb and gel liner may be prevented, thereby protecting the skin on the residual limb from possible abrasion or breakdown.